Move libdng_sdk_validate over to the NDK.

This is used in NDK modules.

I've moved it over to the shared libz since we have an NDK module for
that and this doesn't appear to be used in any static binaries.

Test: make checkbuild tests
Bug: http://b/30465923
Change-Id: I35c27d8a82bbbca21c9eef786ce0ff470b6daddd
1 file changed